Architectural frames

ABSTRACT

A structural frame or frame element, for example for a window is formed of two thin sheet metal members shaped to define a main central hollow shell with two lateral flanges, the two members being rigidly joined at the flanges with intervening thermal insulating strips and the whole of the hollow shell being filled with a rigid lightweight foamed material such as polyurethane which adheres to the shell. In the complete frame joints are formed by hollow connecting sleeves and the foamed material extends through each joint to form a continuous structure. The frame is assembled from Z-section and T-section members of similar dimensions which can thus be joined end-to-end.

United States Patent Cakes May 27, 1975 ARCHITECTURAL FRAMES 3,559,360 2/l97l Bogaert 52/656 [75] Inventor: Thomas Francis Oakes, FOREIGN PATENTS OR APPLICATIONS Cheltenham. England 454,414 6/1968 Switzerland 52/731 {73] Assignee: Martin Bridgewater, Charlton Kings 890513 2,1962 Umted Kmgdom 52/309 Cheltenham Gloucesershire 1,086,032 7/1960 Germany .i 52/725 417,005 l2/l946 Italy 52/73l England; a part interest [22] Filed: July 19, 1973 Primary ExaminerHenry C. Sutherland Appl. N6; 380,916

Continuation of Seri No, 119,590, March I, I97l,

abandoned.

[52] US. Cl. 52/475; 52/393; 52/404; 52/725; 52/758 H [51] Int. Cl.. E04c 3/30; Fl6b 7/18 [58] Field of Search 52/475, 476, 477, 725, 52/731,404, 309,656, 393, 425, 758 H, 409

[56] References Cited UNITED STATES PATENTS 2,9I9,477 l/l960 Schacht 52/476 3,156,332 ll/l964 Cameron 52/73I 3,289,377 l2/l966 Hetman I 52/731 3,455,080 7/1969 Meadows I. 52/476 Attorney, Agent, or Firm-Elliott l. Pollock [57] ABSTRACT A structural frame or frame element, for example for a window is formed of two thin sheet metal members shaped to define a main central hollow shell with two lateral flanges, the two members being rigidly joined at the flanges with intervening thermal insulating strips and the whole of the hollow shell being filled with a rigid lightweight foamed material such as polyurethane which adheres to the shell. In the complete frame joints are formed by hollow connecting sleeves and the foamed material extends through each joint to form a continuous structure. The frame is assembled from Z-section and T-section members of similar dimensions which can thus be joined end-to-end,

5 Claims, 8 Drawing Figures PATENTEm-mzv 1915 3, 5,371

sum [2 OF 3 ATTORNEY PATENTEU my 27 ms SHEET C3UF 3 INVENTOR 30 F P -F/a8,

ATTORNEY ARCHITECTURAL FRAMES This is a continuation, of now abandoned application Ser. No. 119.590. filed Mar. l, 1971.

BACKGROUND OF THE INVENTION This invention relates to structural members, and to building constructions. such as beams, joists, frame sections, space frames, fabricated balustrading, or frames for windows, doors, panels, or other building or architectural constructions. For convenience herein the invention will be defined and described with particular reference to window frames but it will be understood that the invention is of general utility.

Existing frame members are used in the construction of window frames suffer from a number of disadvan tages and it is difficult to meet all the practical requirements without excessive weight or cost. For example a window frame must have adequate strength, the corners and other joints must be rigid, the frame members must have longitudinal and torsional rigidity, the members must be durable, resistant to impact and damage, proof against corrosion, and also preferably should have thermal insulating properties to prevent excessive conduction of heat from the internal to the external surfaces,

Traditional timber and solid section rolled metal frame members fail to meet a number of these requirements, while conventional solid or hollow extruded aluminum or brass frame sections are expensive and also fail to meet many of the requirements. Window frame members have also been constructed in hollow rolled aluminum brass or steel sections, which may be coated to resist corrosion, but in order to provide adequate longitudinal and torsional strength the gauge of the rolled steel sheet must be quite substantial, which results in a heavy and expensive construction. Moreover it is difficult to form corner and other joints since steel members coated with material such as synthetic plastics cannot be welded without damaging the coating.

Various other composite constructions have been proposed but all known constructions are either expensive or fail to meet the optimum design requirements.

Accordingly it is an object of the invention to provide a basic frame section, and also a building construction such as a frame, which will satisfy some if not all of the requirements mentioned above.

SUMMARY OF THE INVENTION Broadly from one aspect the invention consists in a structural member, (particularly but not exclusively a frame section for a window, door, panel, or other build ing or architectural construction) comprising a shell or casing having a wall formed of a thin sheet metal and filled with a rigid foamed material.

The metal shell or casing may be of relatively thin sheet steel having a thickness for example within the range of 0.048 inch to 0.018 inch. More particularly the thickness will conveniently be within the range of 0.036 inch to 0.028 inch and in most practical con structions the preferred thickness is between 0.032 inch and 0022 inch.

Sheet metal such as sheet metal, within these thickness dimensions. does not have adequate thickness to provide the necessary structural integrity for a frame member, but the rigid foam filling together with the metal casing provides an adequately strong and stiff section, The thin metal sheet can easily be formed, for example by cold rolling, to the required profile, and with the rigid internal foam filling provides a durable impact-resistant surface having sufficient strength and rigidity and also to provide for rigid connections between adjacent frame members.

Thus the invention, from this aspect. is based on the concept of providing a thin walled mould casing for the internal foam filling, the mould casing being left in position on the finished product to provide the essential qualities of such a structural member.

The thin metal shell or casing will have only limited thermal conductivity, but in order further to improve the thermal insulation between the internal and external faces of the member the shell or casing is preferably interrupted along two separated joints by thermal insulating material.

The invention also resides in a structure such as a space frame, fabricated balustrading or frame for a window, door, or other building or architectural construction, comprising a number of interconnected structural members or frame sections as defined above.

Conveniently the structural members or frame sections may be filled with foam after assembly, and the rigid foam filling may extend continuously from one frame section to another.

The frame or other construction may include connecting elements inserted into the ends of interconnected frame sections, and in a preferred construction the conecting elements are hollow, and are filled with the foamed material, which thus extends continuously between and interconnects the frame sections,

As stated the invention relates particularly to the manufacture of frames, either fixed or movable, for windows, doors, rooflights or like building or architectural constructions.

The manufacture of a complete suite or range of windows for the building industry presents a number of problems. In addition to the considerable number of sizes that may be required, and the many different combinations of fixed and moving panels and lights, (i.e., glazed panels), each individual light or frame may be mounted in any one of nine or more different manners. A complete suite thus includes at least nine basic different constructions. For example the light may be fixed, or side hung (pivoted on a vertical axis at one side) to open out, or side hung to open in. Likewise the light may be top hung (i.e., horizontally pivoted at its upper edge) to open out, bottom hung to open in, top projected to open out, (i.e., mounted on a pivoted linkage to move downwards and simultaneously swing outwards about a horizontal axis close to its top edge), bottom projected to open in. horizontally center hung, or vertically center hung. In each one of these arrangements the frame sections may have to be arranged to locate the glazing on the outer or inner side. and it will be appreciated that if different frame sections are to be produced for all these different purposes a very large suite will be required, which will greatly increase the overall production costs.

It is known to produce window frame sections in rolled steel, but a complete set of rollers for a rolling mill, for any particular profile is expensive, and hot rolled steel sections suffer from a number of other disadvantages. lf formed of mild steel they are prone to corrosion, and have to be welded, cleaned off, and then galvanized. If formed of stainless steel or other corro sion-resistant material they are likely to be very expensive.

Thus from another aspect the invention consists in a fixed or movable frame element for a window, door, roof-light, or like building or architectural construction, comprising two laterally spaced elongated frame sections or members connected together by an elongated longitudinal joint, the joint including a thermal insulating element located between the two sections. In one form the thermal insulating element itself acts as a structural connecting element and constitutes a jointing member. Alternatively a part of one section may be gripped between two surfaces of a channel or folded portion of the other section, the insulating element being gripped between the opposing surfaces of the two sections.

Preferably the two sections are formed from sheet metal which is rolled or otherwise bent to the required profile, and conveniently the insulating element is in the form of a bridging strip, with a part of each section folded or bent around spaced portions of the strip so that direct thermal contact is avoided. Alternatively the joint may be formed by rolling or otherwise forming a fold in one of the sections, with a part of the other section located within the fold and a layer of thermal insulating material on both sides of the said part.

In any case the two sections are preferably formed to define a hollow section member, and according to a preferred feature the two sections are formed of different materials, chosen respectively for suitability to internal and external conditions. For example the external surface portion may be formed of or coated with a material such as stainless steel, while the internal surface portion is formed of relatively inexpensive mild steel or the like.

In particular preferred form of the invention the sheet metal is steel which is coated on its external surface with a layer of an anti-corrosive material for example a synthetic plastics material such as PVC (polyvinylchloride) or PTFE (polytetrafluoroethylene) or more preferably a polyvinylfluoride plastics (PVFZ). The internal surface of the steel is preferably coated with a material which will provide a good bond with the foamed filling material.

PVFZ is highly inert, and has a long life, and is in many ways an ideal material for building constructions, but is extremely expensive, and normally it is not economical to form structural members in this material by extrusion, or to coat fabricated units with the material. Thus from another aspect the invention is based on the concept of providing a thin coating of a polyvinylflu oride resin on the external surface of a thin metal shell, the shell being filled with a rigid foam.

From another aspect the invention consists in a fixed or movable frame element for a window, door, rooflight, or like architectural or building construction, comprising two frame sections of identical crosssection, arranged and connected together to form a hollow frame element having an inwardly directed flange to locate for example a sheet of glazing material, and an outwardly directed flange to locate against a surrounding wall or a surrounding frame. By using two identical sections, each having a web and two flanges extending in opposite directions, an effective building frame can be constructed very economically. since only one set of forming rolls are required to produce the required profile.

Each frame section is conveniently formed from rolled or otherwise bent sheet metal, and according to a preferred feature of this aspect of the invention each section is generally ofZ shape, with a central web, and two oppositely directed flanges or limbs. Conveniently one limb of the Z is reversely bent to form a groove in which a limb of the other Z-section is located.

From yet another aspect the invention consists in a fixed or movable frame for a window, door, rooflight, or like building or architectural construction, comprising a number of frame elements each formed from two sections of different materials joined lengthwise of the frame element, one section being exposed externally and formed or coated to resist atmospheric corrosion, while the other section is designed and formed to be exposed internally of a building.

From yet another aspect the invention consists in a window, door, rooflight, or like building or architectural construction, comprising a surrounding fixed frame, and an inner moving frame, the frame elements of the two frames all being formed either of a generally Zshaped section or a T-section, with a hollow central element and two lateral limbs.

According to a further aspect of the invention a window, door, or like building construction comprises a surrounding fixed frame, and an inner movable frame, and two frames being formed of sections which are capable of being reversed, i.e., the two sections will match when joined end-to-end so that the inner frame sections are capable of use in a surrounding fixed frame and vice versa. Thus conveniently the sections of both the fixed and movable frames have locating flanges capable of accepting glazing panels.

From yet another aspect the invention consists in a frame section for a window, door, rooflight, or like building or architectural construction, formed with 10- cating formations capable of receiving the edges of glazing panels on both opposite sides.

Preferably the frame section is symmetrical about a plane parallel to the length of the section, and perpendicular to the overall plane of the building construction.

The invention also consists in a suite of windows doors, or like building or architectural constructions, as defined above, all members of the suite being formed principally from two common sections.

Furthermore the invention also resides in a method of manufacturing a building construction, such as a window or door, or a suite of such building constructions, as defined, using two basic frame sections which are reversed or interposed between different parts of the composite construction to provide the required moving frame arrangement.

BRIEF DESCRIPTION OF THE DRAWING The invention may be performed in various ways and a number of embodiments will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a simple diagrammatic front elevation of a typical form of top hinged window construction to which the invention may be applied, including a fixed surrounding frame, and a pivoted inner frame,

FIG. 2 is a detailed sectional view on an enlarged scale on the line IIII in FIG. 1, showing the construction of the fixed and movable frame members in this embodiment of the invention,

FIG. 3 is a fragmentary sectional view, corresponding to part of FIG. 2. showing an alternative form of thermal insulating oint.

FIG. 4 is an end view, partly in section. through a frame member according to the invention, comprising a Z-section member joined end-to-end with a T-seetion member, as used in some forms of pivoting frames,

FIG. 5 is a fragmentary side view of the two members shown in FIG. 4, and illustrating the cut-away or slot in one member to maintain the thermal insulation at the end joint.

FIG. 6 is a fragmentary front elevation. in section on the line VIVI in FIG. 7, of a corner of an assembled frame. illustrating the hollow internal Irshaped con necting member.

FIG. 7 is a sectional end view on the line VIIVII through the corner construction of FIG. 6, and

FIG. 8 is a diagrammatic plan view illustrating an apparatus for injecting foam material into another form of window frame construction according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1 the window construction comprises an outer fixed surrounding frame 10, and an inner movable glazed frame 11, pivoted to the outer frame on a horizontal axis 12 adjacent its upper edge.

FIG. 2 illustrates a crosssection on the line IIII in FIG. 1, through the upper horizontal members of the inner and outer frames. In FIG. 2 the surrounding brickwork is illustrated at 15, the top fixed outer frame member at 16. the top inner frame member at 17, and the glazing (in this example double glazing) at 18. The inner frame member 17 is of T-section, and is designed to close inwardly against the fixed Z-section frame member 16, as the inner frame pivots.

The inner frame member 17 is constructed from two separate longitudinal metal strips indicated generally at 19 and 20, each being rolled or otherwise formed to the illustrated profile. The strip 20 is of generally channel section with two oppositely directed inturned flanges 21, 22 and the strip 19 is generally flat with a narrow central groove 23. and two wings 24, 25, which are folded inwards and doubled over to form inturned folds 26, 27, in a common plane with the inturned flanges 21, 22 of strip 20. A shaped extruded strip of thermal insulating material 28, such as a tough somewhat flexible synthetic plastics, is inserted between each adjajcent pair of folded memtal flanges, the metal flanges being subsequently rolled or clenched over to grip the plastic strip (for example as shown at 29), and so form two rigid longitudinal joints between the two strips 19, 20, each longitudinal joint including a thermal barrier. Since the strip 19 is designed to lie on the external face of the frame, to be exposed to the atmosphere, this may be formed of a suitable non-corrosive material such as stainless steel. The other strip 20 which will then be exposed internally, or less exposed externally. may be formed of a relatively inexpensive material such as mild steel, suitably coated. In order to improve the rigidity of the joint the inturned flanges 21, 22, 26, 27 may be formed vith small spaced projections or ribs to key into the insulating material elements 28.

It will be noted that the strip 20 has a narrow neck formed by two grooves 31, 32 to channel formations 18 the purpose of which will be described more fully below.

The outer fixed frame element 16 is of generally Z- section, and is constructed from two identical metal sections 40 and 41, each of which has a main web 42 with a short perpendicular inturned flange 43 at one end and a wider double inturned folded flange 44 at the other end. Each pair of adjacent folded flanges 43, 44, from two opposite strips are arranged to grip and interlock with an intervening shaped strip of thermal insulating material 45 thus forming two longitudinal joints with thermal insulating barriers, as in the case of the inner frame member 17. Each of the metal strips or sec tions 40, 41, also has an inturned channel or groove 46 similar to the groove 31 in the inner frame member. When the two identical profiles 40, 41 are assembled as shown, and the joints rolled tight, a hollow Z-section frame element 16 is formed which it will be noted has certain basic similarities in profile and dimensions to the hollow T-section member 17. In particular there is a somewhat similar hollow central box frame with two projecting flanges, and the overall dimensions of these parts are identical, but in the case of member 16 the flanges are positioned at diagonally opposite points and extend in opposite directions, whereas in the hollow T- section 17 the two flanges are on the same side. In the hollow Z-section 16 the two elements 40, 41, may be formed of the same or different materials, for example of stainless steel and mild steel, but in any case it will be understood that since they are identical the two profiles can be rolled on the same set of rollers in a rolling mill.

One of the purposes of the grooves 31, 32. 46, is to accommodate flexible plastics sealing strips 50, and it will be noted that the construction allows two such sealing strips to be mounted, one on the inner movable frame member 17 and one on the fixed frame member 16. The other two grooves 32 and 46 are not here used for any specific purpose, but the double glazing unit 18 is located in the inner frame by mastic material 51 and by a clip-on glazing bead 52 secured by poprivets or other fastening devices to the frame member 17.

FIG. 3 illustrates an alternative form of longitudinal thermal insulating joint which may be employed. Instead of the flange 21 on the member 20 being inturned as shown in FIG. 2 the flange is turned outwardly as shown at 55, and likewise the flange 25 on the member 19 is not doubled inwards as shown at 27 in FIG. 2 but is folded back once, as indicated at 56, so as to grip the flange 55 between a double layer of substantially rigid plastics insulating material 57. This alternative form of joint also provides a rigid longitudinal connection between the two metal members, with an intervening thermal barrier.

In the construction of certain types of window, such as center hung pivoting windows, it is necessary that one of the sealing flanges should be reversed from the external to the internal face of the frame member halfway along its length. This can be achieved simply by joining a hollow T-section element such as the member 17 in FIG. 2, to a hollow Z-section element such as member 16, using an internal hollow box section sleeve or cleat of a rigid synthetic plastics material for example, which fits tightly into the hollow box portions of the two frame elements. It is necessary however to maintain the continuity of the thermal barrier, and this would be destroyed if the T and Z-section members are 7 simply butted against each other end-toend. The thermal barrier can however be effectively maintained as shown in FIGS. 4 and 5 by forming a transverse slot or saw cut across the width 61 of the web 62 of one ele ment, and also at the points 63, thus avoiding direct contact between the two flanges. The gap is effectively closed by the internal hollow plastic cleat 66.

FIGS. 6 and 7 illustrate one form of cornerjoint used for connecting two T-section frame members similar to the member 17 of FIG. 2, at the corner of a frame. The two members 70, 71, are both mitred at 45, through their main hollow central portions 72, and also through the two flanges or wings 73, 74. The plastics jointing elements 28 (see FIG. 2) gripped within these double flanges are however cut short at 75, 76, adjacent to the mitred ends of the flanges, and square fillets 77 of plastics material are arranged to enter into the open ends of the flanges on both members 70, 71, thus forming a sealed joint between the respective flanges at the mitred corner. In addition an L-shaped hollow jointing member or cleat 80 is inserted, one limb into the main hollow central part of each of the two members 70, 71, and the corner joint is tightened up by a screw 81 which is passed through a drilling in the member 71, through the hollow cleat 80, and engages in a screw'threaded plastic anchorage member 82, secured by rivets 83 in position in the other member 70. When the corner joint is tight the two limbs of the cleat 80 can be fastened by further rivets 84. It will be noted that the cleat 80 and the anchorage 82 are both hollow and allow the foam filling material to pass through and fill the corner joint, as described in more detail below. Similar constructions may be used for forming T-joints, or for forming joints between Z-seetion members.

Thus it will be seen that the use of two basic profiles, the hollow Z and the hollow T, can be arranged to con struct a wide variety of different frames with fixed and opening lights in a wide variety of different arrangements. The hollow Z profile can be formed from sections produced on a single set of rollers and the hollow T-section can be produced from two rolled profiles. Thus only three sets of rollers are required to form the different sections for the whole range of windows. Since the sections are hollow appreciable strength and torsional rigidity can be achieved using light gauge sheet metal and as explained above the arrangement provides a convenient system for maintaining a thermal barrier without the use of adhesives, welding, rivets or other laborious fabricating methods.

The individual metal sections such as 19, 20, 40, 41 in FIG. 2 are preferably prepared as follows: a length of mild steel strip having a guage thickness preferably within the range of 0.032 inch to 6.022 inch and a width of for example approximately 6 inches, is first continuously hot dip galvanized on both sides, and a rust-inhibitive phosphate priming coat is then applied to one or both faces. A further coating of a bandassisting agent, such as a metal chromate, may be applied to one or both faces, and this agent, or the primer, is selected to be suitable for subsequent coating with PVC or PVFZ on one face and also to form a good bond with polyurethane foam on the other facev One face of the strip, which will be outer surface in the final member, is then given a PVFZ coating, applied in a roller coater. The strip may then be passed through a sto ving oven to cure the PVFZ.

8 Instead of thus treating a relatively narrow strip, a wide strip may be treated and coated in the same manner, and subsequently slit into narrower strips. This will leave exposed bare metal edges, but the preferred 5 method of fabricating the structural member results in these edges being protected.

In any case the prepared coating strip is then passed through a cold roll forming mill to form the strip into the desired section, after which the edges of two suitable strips such as 40 and 41 are rolled over upon each other with intervening plastic inserts 45 to form the rigid longitudinal joints.

In the fabrication of the actual window frame for example the surrounding fixed frame, lengths of the above described section are cut to size and the corners mitred. Hollow angle cleats having two perpendicular limbs, are inserted into the ends of the frame members at the corners and Tjoints, the cleats being designed to fit tightly within the hollow sections. as described above with reference to FIGS. 6 and 7. The whole assembly 89 is then located in a frame 90 as illustrated diagrammatically in FIG. 8, air clamps 91 are applied to force the frame members tightly into contact with one another at the corner and joints, and toggle clamps 92 and anchorages 93 are applied. An injection aperture 94 and air vent aperture 95 are drilled in one or more of the frame members at suitable spaced positions and polyurethane foaming material is then injected through the aperture 94 by means ofa gun 96, to fill the internal cavity, the foaming material also passing through the hollow corner and T-joint cleats 80 to form a continuous solid reinforcing and structural filling. The frame may be heated to assist in the curing of the polyurethane foam, which sets to a rigid condition filling the whole of the frame including the corners and joints.

In another possible construction the preformed frame member may be rolled or otherwise bent around the corners to form a continuous or partly continuous frame. For example in the ease of a circular window such as a porthole the frame member may be rolled from a continuous length to form a circular, oval, or round cornered frame with the two ends butt joined using a hollow internal cleat similar to the cleat 80 of FIG. 6.

In many constructions the metal shell or mould will form a continuous closed hollow section but in some cases it may be preferred to leave a gap in the wall, particularly for use in the external surface of a fixed window frame to be located in masonry. In such case the gap between the two edges of the metal shell is preferably closed temporarily by a closure strip having an in ternal surface coating of a release agent such as polythene which will not bond to the polyurethane of the foam filling. After the internal cavity has been filled with the foam this temporary strip is removed.

As mentioned the foam filling should be rigid and of sufficient strength to act as a structural part of the whole member. This permits very thin sheet metal to be used, of the thicknesses specified. The preferred forming material is polyurethane in which case the density is preferably between about 2.5 pounds per cubic foot and 10 pounds per cubic foot especially good results are obtained with the foam density in the range of 3.5 to 5.5 pounds per cubic foot. Polyurethane is also an excellent adhesive and the use of a foaming material which is also an adhesive is important in the construction of strong joints, for example at the corners. The pressure of the foam drives the polyurethane into all the small crevices where it adheres strongly. ln addition of course each joint includes an internal hollow sleeve or connecting piece, such as 82, which may be formed of a material such as nylon having considerable strength, and which is itself coated with an adhesive before insertion so as to adhere to the two sections,

I claim:

l. A rectangular architectural frame comprising a plurality of elongated hollow structural members rigidly connected together at their ends to provide corners for said frame, each said member being formed from two elongated thin sheet metal parts shaped to define an internal cavity having two laterally projecting flanges extending outwardly from two corners of said cavity, said two sheet metal parts being spaced from one another and being connected together by two seam joints which extend along the longitudinal edges of said sheet metal parts and which are located respectively within said flanges in spaced relation to said cavity, each said seam joint including a layer of thermal insulating material located between the adjacent edges of said two metal parts to keep said edges spaced from one another and to provide a thermal barrier therebetween, each edge of each said sheet metal part being folded over at each said seam and being indirectly interlocked with the adjacent folded edge of said other part through said layer of thermal insulating material which includes portions interleaved respectively between said folded over edges of said sheet metal parts, the extreme edges of both said sheet metal parts being concealed within said seam joints, and a completely concealed hollow L-shaped internal connecting piece at each corner of said frame, said connecting piece being fabricated of a synthetic plastic thermal insulating material and having two hollow limbs correspond ing in shape to the interiors of said hollow structural members and communicating with one another, said limbs respectively fitting into and concealed within the open ends of the respective two hollow structural members at said corner, means connecting each of said hollow limbs to its respective structural member, the said internal cavity of said frame being filled with a rigid synthetic foam material which extends continuously around the interior of the frame and through said hollow internal connecting pieces at the corners of the frame.

2. The frame of claim 1 including at least one insulating insert at each corner of said frame having portions which extend into the ends of the two seam joints adjacent said corner.

3. The frame of claim 1 wherein said cavity is sub stantially rectangular, said two laterally projecting flanges extending from adjacent corners of said cavity and lying in a common plane.

4. The frame of claim 1 wherein said cavity is substantially rectangular, said two laterally projecting flanges extending from diagonally opposite corners of said cavity and lying in parallel planes,

5. A frame according to claim 1 wherein one of said sheet metal parts is formed of mild steel and the other said part is formed of stainless steel 

1. A rectangular architectural frame comprising a plurality of elongated hollow structural members rigidly connected together at their ends to provide corners for said frame, each said member being formed from two elongated thin sheet metal parts shaped to define an internal cavity having two laterally projecting flanges extending outwardly from two corners of said cavity, said two sheet metal parts being spaced from one another and being connected together by two seam joints which extend along the longitudinal edges of said sheet metal parts and which are located respectively within said flanges in spaced relation to said cavity, each said seam joint including a layer of thermal insulating material located between the adjacent edges of said two metal parts to keep said edges spaced from one another and to provide a thermal barrier therebetween, each edge of each said sheet metal part being folded over at each said seam and being indirectly interlocked with the adjacent folded edge of said other part through said layer of thermal insulating material which includes portions interleaved respectively between said folded over edges of said sheet metal parts, the extreme edges of both said sheet metal parts being concealed within said seam joints, and a completely concealed hollow L-shaped internal connecting piece at each corner of said frame, said connecting piece being fabricated of a synthetic plastic thermal insulating material and having two hollow limbs corresponding in shape to the interiors of said hollow structural members and communicating with one another, said limbs respectively fitting into and concealed within the open ends of the respective two hollow structural members at said corner, means connecting each of said hollow limbs to its respective structural member, the said internal cavity of said frame being filled with a rigid synthetic foam material which extends continuously around the interior of the frame and through said hollow internal connecting pieces at the corners of the frame.
 2. The frame of claim 1 including at least one insulating insert at each corner of said frame having portions which extend into the ends of the two seam joints adjacent said corner.
 3. The frame of claim 1 wherein said cavity is substantially rectangular, said two laterally projecting flanges extending from adjacent corners of said cavity and lying in a common plane.
 4. The frame of claim 1 wherein said cavity is substantially rectangular, said two laterally projecting flanges extending from diagonally opposite corners of said cavity and lying in parallel planes.
 5. A frame according to claim 1 wherein one of said sheet metal parts is formed of milD steel and the other said part is formed of stainless steel. 